Creative Commons

also referred to as a Share-alike license

Creative Commons is the name of a nonprofit corporation
that makes it easier for people to share and build upon the
work of others, consistent with the rules of copyright. The organization provides free licenses (and other legal tools) to
mark creative work with the freedom the creator wants it to carry, so
others can share, remix, or use commercially other people's work, including literature, music and photography.

A Creative Commons license provides a flexible range of protections and freedoms for authors, artists, and educators, and a range of options regarding the kind of rights they wish to maintain or give away. Choices include:

Let others download and share your work, but not permit them to change it or use it commercially,

Allow other no only to download and share, but also to remix or tweak, as long as you are credited and users license their new product under the same terms you have,

Permit downloading, sharing, and revising (as long as you are credited) but also authorize those creating derivative works to profit commercially.